This study compared multiple airway dimensions from CT images between RS patients demonstrating normal or difficult intubation during MDO to identify factors useful for presurgical prediction of difficult airway management. Over half of this patient cohort exhibited difficult intubation, and such patients demonstrated a shorter distance between the root of the tongue and posterior pharyngeal wall (D6), a shallower bilateral mandibular angle (A5), and smaller cross-sectional area at the epiglottis tip (Table 3). Based on these findings, we established a clinical prediction rule and verified its efficacy by ROC curve analysis. While tongue root to posterior pharyngeal wall distance (D6) differed significantly between groups, it is also influenced by tongue movement and so may not be reliable for clinical applications. Similarly, many hospitals lack the technology for routine three-dimensional reconstruction of CT images, limiting the use of A5. Therefore, in an attempt to simplify the CT composite score for routine clinical use, we constructed a decision tree model based only one cross-sectional area at the epiglottis tip (Fig. 3) as this metric is not influenced by tongue movement and may be measurable using radiation-free techniques, such as MRI. ROC analysis of this parameter yielded a high AUC (0.8125) using a cut-off cross-sectional area of 36.97 mm2, indicating that a cross-sectional area above 36.97 mm2 is predictive of difficult intubation.
Mallampati score, nail−chin spacing, chest−chin spacing, upper and lower incisor spacing, mandibular protrusion, cervical retroversion, and ratio of thyromental height to distance are the most widely used methods to identify laryngoscopic exposure difficulties [20,21,22,23,24,25]. However, most of these methods were established by screening the general population, and are not applicable for patients with maxillofacial deformities . Robin sequence patients have unusual and highly heterogeneous jaw and upper airway morphologies, making it difficult to predict difficult intubation. Computed tomography can be used to evaluate infant bony and soft tissue anatomy of the upper airway in 2 and 3 dimensions, which is not possible with cephalometrics [27,28,29]. While CT scanning does require radiation exposure, maxillofacial CT is a routine preoperative examination for MDO [16,17,18], so this evaluation method will not require additional exposure. Further, cone-beam delivery can markedly reduce total radiation dose, so there is no additional safety limitation for clinical practice. Surgical treatment is often unavoidable for the treatment of severe RS , and early identification of difficult intubation will help reduce complications from multiple intubation attempts.
This is an exploratory study and has several limitations. First, we were unable to observe the effects of mouth opening on glottic exposure in children with oral closure and quiet breathing during CT scan. The small sample size also limits statistical strength, so other factors predictive of difficult intubation may have been missed. However, we did try to minimize the impact of growth, development, and age through normalization of the CT metrics to baseline values. In addition, this study was conducted at a single center, which may introduce selection bias. For instance, these CBCT metrics were derived from RS infants with severe airway obstruction, and it is not clear whether they persist in infants with mild airway obstruction. However, only severe RS patients require presurgical intubation, so we believe that patient selection does not limit the clinical applicability of the prediction rule. Severe RS patients who need MDO all have potentially life-threatening breathing difficulties. In order to minimize the risk of airway obstruction, our hospital stipulates no more than two attempts at laryngoscopic visualization and intubation. Therefore, we have no clinical information on patients with three or more unsuccessful intubation attempts. This is why patients were divided into normal and difficult intubation groups according to Cormack−Lehane classification instead of by the number of laryngoscopic visualization and intubation attempts.
This work represents a first step toward development of an evidence-based decision tool for predicting difficult intubation in patients with RS, but prospective validation is needed. To further advance our understanding of factors conferring difficult intubation in children with RS, we plan to compare other airway and bone measurements as well as clinical severity measurements. Future work should also assess the effectiveness of imaging modalities that do not involve ionizing radiation, such as MRI.